1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to discriminating a type of packet loss occurring in wireless transmission, and more particularly, to determining whether the packet loss is wireless loss or congestion loss.
2. Description of the Related Art
When a high-bitrate video stream is transmitted over a wireless local area network (LAN) complying with Institute of Electrical and Electronics Engineers (IEEE) 802.11, the transmission is generally performed in such a way to appropriately cope with a loss that may occur during the transmission. For example, if wireless loss occurs during the transmission of a high-bitrate video stream, the high-bitrate video stream is transmitted after an error correction code is added to the high-bitrate video stream. On the other hand, if congestion loss occurs during the transmission of a high-bitrate video stream, the high-bitrate video stream is transmitted after the bitrate of the high-bitrate video stream is reduced.
FIGS. 1A and 1B illustrate a related art single stream transmitting/receiving system.
Referring to FIGS. 1A and 1B, the related art single stream transmitting/receiving system includes a transmitter 11, a router 12, an access point (AP) 13, and a receiver 14.
The transmitter 11 transmits packets corresponding to a single stream through the Internet in a wired manner. Thus, the transmitter 11 may be regarded as a server. The router 12 receives packets from the transmitter 11 and routes the packets to their destination, i.e., the receiver 14, based on the Internet protocol (IP) addresses of the packets. The AP 13 receives packets from the router 12, buffers the received packets, and continuously transmits the buffered packets through an IEEE 802.11 wireless LAN in a wireless manner. Thus, the AP 13 may be regarded as a base station including both a wired communication module and a wireless communication module. The receiver 14 receives packets from the AP 13. Thus, the receiver 14 may be regarded as a client.
First, wireless loss illustrated in FIG. 1A will be considered.
The transmitter 11 transmits packets 1 through 3 in a wired manner. The router 12 receives the packets 1 through 3 from the transmitter 11 and routes the packets 1 through 3. The AP 13 receives the packets 1 through 3 from the router 12 and transmits the packets 1 through 3 in a wireless manner. At this time, during the wireless transmission of the packets 1 through 3 from the AP 13 to the receiver 14, the packet 2 is lost due to 2.4 GHz microwaves radiated from a microwave oven. As a result, the receiver 14 only receives the packets 1 and 3.
Such a case is called wireless loss. In this case, since the packet 2 is lost while being transmitted from the AP 13 to the receiver 14 in a wireless manner, the arrival interval between the packets 1 and 3 is 2T when a packet interval is T.
Next, congestion loss illustrated in FIG. 1B will be considered.
The transmitter 11 transmits packets 1 through 3 in a wired manner. At this time, during the transmission of the packets 1 through 3 from the transmitter 11 to the router 12, the transmission of the packet 2 is congested due to a difference between bandwidths of the transmitter 11 and the router 12 and thus the packet 2 is lost. As a result, the router 12 only receives the packets 1 and 3 and routes the packets 1 and 3. The AP 13 receives the packets 1 and 3 from the router 12 and transmits the packets 1 and 3 in a wireless manner. The receiver 14 receives the packets 1 and 3.
Such a case is called congestion loss. In this case, since the packet 2 is lost while being transmitted from the transmitter 11 to the router 12 in a wired manner and the packets 1 and 3 are buffered by the AP 13, the arrival interval between the packets 1 and 3 is T when a packet interval is T.
According to a related art method for discriminating the type of packet loss, the arrival interval between packets is measured. If the measured arrival interval satisfies (N+1)Tmin<=arrival interval<(N+2)Tmin, the type of packet loss is determined to be wireless loss. Otherwise, the type of packet loss is determined to be congestion loss. Tmin indicates the minimum arrival interval among the measured arrival intervals and N indicates the number of lost packets. Thus, in the above example, Tmin is T and N is 1.
The related art method for discriminating the type of packet loss is based on the following assumptions. First, packets correspond to a single stream having a constant bitrate. Second, each of the packets has the same size. Third, the AP 13 continuously transmits the packets at regular intervals. Fourth, the bandwidth of wired transmission is much larger than that of wireless transmission. Fifth, the router 12 adopts a drop mechanism to drop a packet when packet transmission is congested.
However, the related art method for discriminating the type of packet loss is not suitable for discriminating the type of packet loss for packets corresponding to a plurality of streams such as multi-streams, in particular, multi-video streams. This is because an interval between packets corresponding to one of the multi-streams is not constant due to the intervention of packets corresponding to another one of the multi-streams. Moreover, an interval between packets corresponding to one of multi-video streams may not be constant due to the fluctuation of an effective bandwidth and changes in the transmission bitrate of transmitters.